I have seating dies from RCBS, Gold Medal and Competition, the 30/06 seater die is 30 cal specific, the problem with using the seater die for the 308 Winchester is the case is too short to reach the top of the die, to save money on expensive seater dies a reloader can purchase one die to seat 30/06 and add an extended shell holder to seat 308 Winchester and an 8mm bullet guide to seat 8mm57 bullets, money goes further that way.
There are extended shell holders that are designed to be used when forming cases, those shell holders will not have a primer exit hole, Herters sold shell holders with out holes for the primer to exit, the Herters shell holder was designed to be used in a press when swagging bullets.
F. Guffey